Plasma processing has been widely used in the semiconductor and other industries for many decades. Plasma processing is used for tasks such as cleaning, etching, milling, and deposition. More recently, plasma processing has been used for doping. Plasma doping systems have been developed to meet the doping requirements of some modern electronic and optical devices. Plasma doping is sometimes referred to as PLAD or plasma immersion ion implantation (PIII).
Plasma doing is fundamentally different from conventional beam-line ion implantation systems that accelerate ions with an electric field and then filter the ions according to their mass-to-charge ratio to select the desired ions for implantation. Plasma doping systems immerse the target in a plasma containing dopant ions and bias the target with a series of negative voltage pulses. The electric field within the plasma sheath accelerates ions toward the target which implants the ions into the target surface.
Ion implantation and other doping systems for the semiconductor industry generally require a very high degree of uniformity. Conventional beam-line ion implantation systems used in the semiconductor industry provide excellent uniformity across the entire surface of state-of-the art semiconductor substrates. In general, the uniformity of plasma doping systems is not as good as conventional beam-line ion implantation systems. Many plasma doping systems have at least some radial non-uniformities in dosing. The radial non-uniformity in dosing often results in higher doses toward the center of the substrate or higher doses near the edge of the substrate.